The proposal encompasses two lines of investigation. The major one, projected for a 5-year period, is concerned with sexual behavior and physiology in Culicoides, using C. melleus as the experimental animal. The overall objective is to give a complete account of sexual behavior in C. melleus and to investigate and describe all other processes, functional, anatomical, sensory and physiological, associated with the sexual act. Methods will vary considerably according to the specific nature of the problem. Established techniques will be employed in microanatomical and histological work. Behavioral bioassay will form the basis of reference in much of the behavioral work. Event recorders and video recordings will be used for quantitative estimation of behavior. Some experiments will involve blockage of sense organs to determine function. Efficiency of sperm transfer and male potency will be assessed by counting stained spermatozoa. The more limited lines of investigation will be concerned with larval behavior and oviposition in C. melleus and C. furens. Observations on larval behavior will initally involve more detailed studies of the distribution of C. melleus larvae in the natural habitat in conjunction with automatically monitored (Biopulse) activity studies under controlled laboratory conditions. Laboratory experiments to test preferences for physical and chemical conditions are planned. The study of oviposition will begin with examination and description of the act of egg-laying itself. Experimental work will be concerned with periodicity of oviposition in response to environmental conditions and with factors that induce oviposition.